I'm using Python 2 to parse JSON from ASCII encoded text files.

When loading these files with either json or simplejson, all my string values are cast to Unicode objects instead of string objects. The problem is, I have to use the data with some libraries that only accept string objects. I can't change the libraries nor update them.

Is it possible to get string objects instead of Unicode ones?

Example

>>> import json
>>> original_list = ['a', 'b']
>>> json_list = json.dumps(original_list)
>>> json_list
'["a", "b"]'
>>> new_list = json.loads(json_list)
>>> new_list
[u'a', u'b']  # I want these to be of type `str`, not `unicode`

Update

This question was asked a long time ago, when I was stuck with Python 2. One easy and clean solution for today is to use a recent version of Python — i.e. Python 3 and forward.

While there are some good answers here, I ended up using PyYAML to parse my JSON files, since it gives the keys and values as str type strings instead of unicode type. Because JSON is a subset of YAML it works nicely:

>>> import json
>>> import yaml
>>> list_org = ['a', 'b']
>>> list_dump = json.dumps(list_org)
>>> list_dump
'["a", "b"]'
>>> json.loads(list_dump)
[u'a', u'b']
>>> yaml.safe_load(list_dump)
['a', 'b']

Notes

Some things to note though:

• I get string objects because all my entries are ASCII encoded. If I would use unicode encoded entries, I would get them back as unicode objects — there is no conversion!

• You should (probably always) use PyYAML's safe_load function; if you use it to load JSON files, you don't need the "additional power" of the load function anyway.

• If you want a YAML parser that has more support for the 1.2 version of the spec (and correctly parses very low numbers) try Ruamel YAML: pip install ruamel.yaml and import ruamel.yaml as yaml was all I needed in my tests.

Conversion

As stated, there is no conversion! If you can't be sure to only deal with ASCII values (and you can't be sure most of the time), better use a conversion function:

I used the one from Mark Amery a couple of times now, it works great and is very easy to use. You can also use a similar function as an object_hook instead, as it might gain you a performance boost on big files. See the slightly more involved answer from Mirec Miskuf for that.

There's no built-in option to make the json module functions return byte strings instead of unicode strings. However, this short and simple recursive function will convert any decoded JSON object from using unicode strings to UTF-8-encoded byte strings:

def byteify(input):
    if isinstance(input, dict):
        return {byteify(key): byteify(value)
                for key, value in input.iteritems()}
    elif isinstance(input, list):
        return [byteify(element) for element in input]
    elif isinstance(input, unicode):
        return input.encode('utf-8')
    else:
        return input

Just call this on the output you get from a json.load or json.loads call.

A couple of notes:

• To support Python 2.6 or earlier, replace return {byteify(key): byteify(value) for key, value in input.iteritems()} with return dict([(byteify(key), byteify(value)) for key, value in input.iteritems()]), since dictionary comprehensions weren't supported until Python 2.7.
• Since this answer recurses through the entire decoded object, it has a couple of undesirable performance characteristics that can be avoided with very careful use of the object_hook or object_pairs_hook parameters. Mirec Miskuf's answer is so far the only one that manages to pull this off correctly, although as a consequence, it's significantly more complicated than my approach.